The instant invention relates to tire grinding machines and more particularly to sensor shoes which locate the surface of tires.
Improvement of force variation on pneumatic tires is done on uniformity machines known as tire uniformity grinders or tire uniformity optimizers. Generally, small truck tires, unlike many conventional passenger tire tread designs, are "luggy" and present an interrupted or discontinuous surface along their periphery, particularly in the shoulder region. This type of tread design, as well as tread designs of traction-type tires and so-called mud and snow tires, create special problems when processed through the tire uniformity machines.
Tire uniformity machines are equipped with two or three grinding wheels. In the case of two grinding wheels each of the wheels is located in a position essentially adjacent to each tire shoulder (a spacing of about 0.001 or 0.002 inch between the grinding wheel and the tire being preferred). In the case of three grinding wheels, such as disclosed in U.S. Pat. No. 3,841,033, a third grinding wheel located essentially contiguous to the central portion of the tire tread, is added to the two-wheel machines. Immediately in front of the grinding wheels are sensors, each with a suitable reference pick-up or probe. The essential purpose of this reference probe is to find the surface of the tire.
The tire uniformity machines presently available are equipped with standard sensor shoes for tracking tire tread surfaces. These shoes perform reasonably well on passenger tires with conventional treads. However, when they are used on lug-type tire treads they drop into and out of the grooves between the lugs as the sensor attempts to track the rotating tire, which may be rotating at a speed of 60 revolutions per minute or more. The rapid up and down movement of the sensors causes the grinding wheels to chatter, which frequently results in damaged treads, such as chunk-out or rounding-off of the edges of the lugs. In some cases the sensors and grinding assembly may become damaged.
Heretofore, the shape of the sensor shoe or probe was not critical and was usually not more than a point. However, with recent requirements for improvement in force variation in pneumatic tires, the prior art sensor shoe was proven inadequate. The present invention therefore provides a sensor shoe with a unique, arcuately contoured shape, which tracks the tire tread surface and bridges any intermittent voids or grooves along the surface to tires.